This invention broadly relates to the preparation of closed cell phenolic resin foams produced from compositions of phenol-aldehyde resole resins, and the foam products thus prepared. More particularly the present invention relates to the preparation of phenolic resin foams by a method employing a novel modified phenolic foam catalyst. The invention also relates to these modified phenolic foam catalysts.
The manufacture of phenolic foams is achieved by intimately mixing a phenolic resin with an acid catalyst, a surface active agent and a blowing agent. The phenolic resins generally used are resoles which, under the influence of an acid catalyst, undergo further condensation to produce an infusible thermoset material. The rate of this condensation or `cure` is determined by the nature and quantity of acid catalyst and the rate of production and removal of volatile condensation products, such as formaldehyde and water.
Typical acid catalysts used in the manufacture of phenolic resin foams are the aromatic sulfonic acids, such as xylene --toluene sulfonic acids (ULTRA TX --trademark of Witco Chemicals), or phenol sulphonic acid. These acids are generally used in the 10% to 25% level to achieve commercially acceptable cure times in the manufacture of phenolic resin foams. These levels of acid catalysts lead to high exotherm temperatures and a pronounced moisture sensitivity in the final product.
In the manufacture of closed cell phenolic foams, such high exotherm temperatures necessitate the use of pressure during the expansion process to prevent `rupture` of the cell windows. This bursting Of the cells is caused by the high vapour pressures generated by the presence of the blowing agent, along with volatile condensation products, such as water and formaldehyde. Thus Doerge in U.S. Pat. No. 4,423,168 dated Dec. 27, 1983 and entitled "Method of Producing Phenolic Foam Using Pressure and Foam Produced by the Method" discloses a method for making a phenolic foam whereby the phenolic resole resin foamable composition is introduced into a substantially closed volume and foamed under pressure in excess of two pounds per square inch.
In addition, these acid levels induce a degree of moisture sensitivity which creates problems with regard to dimensional and thermal stability of the resultant foam.
The above deficiencies have severely limited the commercial utility of closed cell phenolic foams. Attempts to reduce the peak temperature, and moisture sensitivity by reducing the acid level, as described in European Patent Nos. 006967 and 006968, both to Monsanto, lead to extended set and cure times, making the manufacturing process slow.
Several references of prior art disclose resorcinol as a reactant with the resole resin itself. Among those is the closed cell phenolic foam described in U.S. Pat. No. 4,546,119, dated Oct. 3, 1985 by inventors J. Lunt, E. J. MacPherson and P. J. Meunier, and assigned to the same assignee. This reference discloses a method of making a phenolic foam material by reacting the phenol-formaldehyde resole with resorcinol, urea or both prior to initiating foam formation by acid catalysis.
Canadian Patent No. 859,789 to Pretot, issued Dec. 29, 1970 and entitled, `Phenolic Resin Foams` discloses a method of manufacture of phenolic foams including the addition of resorcinol to the phenol formaldehyde resin and blowing agent prior to the addition of strong acid which is last. Resorcinol, in this case, was found to reduce the amount of acid required for foam formation.